Foam-based substrate for catalytic converter

ABSTRACT

A substrate for a catalytic converter, comprising an open cell carbon foam having a geometric surface area of at least about 5000 m 2 /m 3  and a permeability of at least about 8.0 darcys.

TECHNICAL FIELD

The present disclosure relates to the field of catalytic converters forautomobiles and other vehicles, where the catalytic converters utilizecarbon foam as the substrate for catalyst particles. More specifically,the present disclosure relates to foam-based substrates including noblemetal catalysts and/or non-noble metal nanomaterial catalysts forcatalytic converters.

BACKGROUND

Internal combustion engine exhaust contains environmentally andbiologically harmful compositions, including hydrocarbons, carbonmonoxide, and nitrogen oxide which arise from combustion of gasoline orother fuels. Catalytic converters were developed for vehicles to reducethe emission of these harmful compositions, and, in the U.S., have beeninstalled on passenger cars and light-duty trucks since 1975.

Catalytic converters reduce vehicle exhaust emission levels bychemically converting engine-out emissions before the exhaust gas leavesthe tailpipe. Conventionally, a catalytic converter contains a“honeycomb” ceramic substrate housed in a stainless steel canister thatdirects exhaust gases through narrow channels. A catalyst layer isapplied to the surface of the channels and facilitates the conversion ofpollutants primarily into water vapor, carbon dioxide, and nitrogen. Thecatalysts employed in most cases are noble metals, such as platinum(Pt), rhodium (Rh), and palladium (Pd).

Current catalytic converters are commonly referred to as three-waycatalytic converters due to the three simultaneous reactions occurringover the catalyst. These include two oxidation reactions to reducehydrocarbons (HC) and carbon monoxide (CO) and a reduction reactioninvolving oxides of nitrogen (NOx) with CO over a suitable catalyst toreduce NOx to nitrogen gas and carbon dioxide.

The exact combination of catalytic metals differs according to the levelof engine-out emissions and the required emission reductions. Currentcatalytic converter designs are more than 95% efficient in removing HCsand CO, and at least 85% effective at reducing NOx over the lifetime ofthe converter.

Traditionally, catalytic converters are prepared by separately mixingoxidative precious metals, such as platinum or palladium, with aluminumoxide, water, and other components to make a slurry in one container andmixing one or more reductive precious metals, such as rhodium, withcerium zirconium oxide, water, and other components to make a secondslurry in a second container. The slurries are normally referred to asoxidative and reductive washcoats. A ceramic monolith, which can becylindrically shaped, having a grid or “honeycomb” array structure, isdipped into one of the washcoats to form a first catalytic layer on themonolith. After drying and calcining, the ceramic monolith is dippedinto the other washcoat to form a second layer. The ceramic monolith isthen fitted into a shell of a catalytic converter, which connects to theengine for treating exhaust gas.

BRIEF SUMMARY

The present disclosure relates to open cell carbon foam substrates foruse in catalytic converters. By “open cell” is meant that the pores ofthe foam are interconnected (rather than sealed), allowing gases orother fluids to flow therethrough. The substrates can provide for moreuniform gas flow as compared to conventional ceramic monoliths, whileallowing for improved contact with catalyst particles.

More particularly, a purpose of the substrate is to provide a relativelylarge geometric surface area (GSA). This is because the GSA of asubstrate for a catalytic converter is a key factor in determining boththe quantity of the catalyst that is required and the conversionefficiency of the converter. A higher GSA makes it possible to reducethe quantity of catalyst and increase the contact between the catalystand the exhaust gas.

In some embodiments, the GSA of the substrate of the present disclosureis at least about 5000 m²/m³. In other embodiments, the GSA is at leastabout 8000 m²/m³, or even at least 15,000 m²/m³ or higher. In someembodiments, the GSA is up to about 35,000 m²/m³. Thus, in embodiments,the GSA of the substrate of the present disclosure can range from about5000 m²/m³ to about 35,000 m²/m³, or 8000 m²/m³ to about 35,000 m²/m³,or even 15,000 m²/m³ to about 35,000 m²/m³.

Carbon foam for use as a substrate for catalytic converters has adensity of about 0.03 to about 0.9 grams per cubic centimeter (g/cc),with a surface area of about 200 to about 900 square meters per gram(m²/g). In an embodiment, the compressive strength of the foam should beat least about 35 kilograms per square centimeter (kg/cm²)(measured by,for instance, ASTM C695).

The use of the foam substrate of this disclosure should engender apressure drop of no greater than about 300 Pa, and, in embodiments, fromabout 25 to about 300 Pa; in certain embodiments, the pressure dropengendered by the carbon foam substrate of the present disclosure shouldbe no greater than about 90 Pa, and can be from about 50 to about 90 Pa.In other embodiments, the foam substrate of this disclosure should leadto a pressure drop of no greater than 80% of the pressure drop observedwhen a conventional catalytic converter is employed in its place. Forexample, at conventional exhaust velocities exiting the engine (taken tobe 0.025 m³/s), a conventional catalytic converter creates a pressuredrop of at least about 150 Pa; sometimes the observed pressure drop ishigher than 200 Pa. The catalytic converter of this disclosure, at thoseexhaust velocities, should provide a pressure drop of no greater than120 Pa. In certain embodiments the pressure drop is less than 90 Pa.

The carbon foam should, in some embodiments, have a relatively uniformdistribution of pores in order to provide relatively consistent gas flowtherethrough. In addition, in certain embodiments the pores arerelatively isotropic, by which is meant that the pores are relativelyspherical and have, on average, an aspect ratio of between about 1.0(which represents a perfect spherical geometry) and about 1.5. Theaspect ratio is determined by dividing the longest dimension of any porewith its shortest dimension. The foam should, in some embodiments, havea total porosity of about 65% to about 95%, more preferably about 70% toabout 95%.

In some embodiments, the carbon foam useful as a catalytic convertersubstrate exhibits a permeability of at least about 8.0 darcys; in otherembodiments the carbon foam has a permeability of at least than about15.0 darcys (as measured, for instance, by ASTM C577). In yet otherembodiments, the carbon foam of this disclosure exhibits a permeabilityof at least about 20.0 darcys. From a practical standpoint, the foam hasa permeability of from about 15.0 darcys to about 35.0 darcys.

DETAILED DESCRIPTION

Carbon foams for use as catalytic converter substrates can be formed ofa variety of materials, in a variety of ways, provided they meet therequirements detailed herein. For instance, in some embodiments thefoams can be formed from polymeric foams, such as phenolic orpolyurethane foam, as starting materials as discussed in US ApplicationPublication No. 2010/0104496 and U.S. Pat. No. 3,387,940. In otherembodiments, the foam starting materials can be formed frompolyacrylonitrile (PAN) or other acrylonitrile materials, as disclosedby U.S. Pat. No. 4,832,881. Other starting materials that can be used insome embodiments are derived from organic gels which may be preparedfrom hydroxylated benzenes (such as phenol, catechol, resorcinol,hydroquinone, and phloroglucinol) and aldehydes (such as formaldehydeand furfural), as discussed in U.S. Pat. No. 5,945,084.

Phenolic and Polyurethane Polymeric Foams

In an embodiment, to produce catalytic converter substrate of thepresent disclosure from polymeric foams, a polymeric foam block,particularly a phenolic foam block, is carbonized in an inert orair-excluded atmosphere, at temperatures which can range from about 500°C., more preferably at least about 800° C., up to about 3200° C.

The foam is prepared by adjusting the water content of the resin andadding a surfactant (e.g., an ethoxylated nonionic), a blowing agent(e.g., pentane, methylene chloride, or chlorofluorocarbon), and acatalyst (e.g., toluenesulfonic acid or phenolsulfonic acid). Thesulfonic acid catalyzes the reaction, while the exotherm causes theblowing agent, emulsified in the resin, to evaporate and expand thefoam. The surfactant controls the cell size as well as the ratio ofopen-to-closed cell units.

The preferred phenol is resorcinol. However, other phenols of the kindwhich are able to form condensation products with aldehydes can also beused. Such phenols include monohydric and polyhydric phenols,pyrocatechol, hydroquinone, alkyl substituted phenols, such as, forexample, cresols or xylenols; polynuclear monohydric or polyhydricphenols, such as, for example, naphthols, p,p′-dihydrexydiphenyldimethyl methane or hydroxyanthracenes.

The phenols used to make the foam starting material can also be used inadmixture with non-phenolic compounds which are able to react withaldehydes in the same way as phenol.

The preferred aldehyde for use in the solution is formaldehyde. Othersuitable aldehydes include those which will react with phenols in thesame manner. These include, for example, acetaldehyde and benzaldehyde.

In general, the phenols and aldehydes which can be used in this processare those described in U.S. Pat. Nos. 3,960,761 and 5,047,225.

The polymeric foam used as the starting material in the production ofthe carbon foam should have an initial density which mirrors the desiredfinal density for the carbon foam which is to be formed.

As noted, in order to convert the polymeric foam to carbon foam, thefoam is carbonized by heating to a temperature of from about 500° C.,more preferably at least about 800° C., up to about 3200° C., in aninert or air-excluded atmosphere, such as in the presence of nitrogen.The heating rate should be controlled such that the polymer foam isbrought to the desired temperature over a period of several days, sincethe polymeric foam can shrink by as much as about 50% or more duringcarbonization. Care should be taken to ensure uniform heating of thepolymer foam piece for effective carbonization.

By use of a polymeric foam heated in an inert or air-excludedenvironment, a non-graphitizing glassy carbon foam is obtained, whichhas the approximate density of the starting polymer foam. The carbonfoam has a relatively uniform distribution of isotropic pores having, onaverage, an aspect ratio of between about 1.0 and about 1.5.

In other embodiments, the polymeric foam-based carbon foam of thepresent disclosure can be a rigid polyurethane foam of the polyestertype. These foams can be prepared by reacting a polyester with anorganic polyisocyanate. Polyesters that are suitable reactants with thepolyisocyanates are those having reactive hydrogen-containing terminalgroups, preferably predominantly hydroxyl groups. The hydroxyl number ofthe polyester is in the range from about 100 to about 600.

Typical polyesters are propylene glycol, ethylene glycol, glycerol,reaction products of polyols such as aliphatic polyols, i.e.,polyethylene glycols, polypropylene glycols, polybutylene glycols,polyoxyethyleneoxybutylene glycols, polyoxypolypropyleneoxybutyleneglycols, 1,2,6-hexane triol, 1,1,1-trimethylolpropane, and the like,with a polycarboxylic acid such as oxalic acid, succinic acid, maleicacid, adipic acid, sebacic acid, isosebacic acid, phthalic acid, and thelike. Other useful polyesters comprise homopolymers of lactones, notablyepsilon, caprolactones, started with a reactive hydrogen-containingcompound, Such as those disclosed in U.S. Pat. No. 2,914,556. A varietyof organic polyisocyanates may be employed for reaction with theabove-described polyesters to provide suitable rigid urethane foams, aswould be familiar to the skilled artisan.

Preparation of the foam can be carried out by the one-shot orsemi-prepolymer techniques, each of which are well known. In thesemi-prepolymer technique, the polyester reactant is partially extendedwith excess isocyanate to provide a reaction product containing a highpercentage of free isocyanate groups (20 to 35%) which is foamed at alater stage by reaction with additional polyester, catalyst and ablowing agent. In the one-shot technique, all of the reactants arereacted simultaneously with the foaming operation.

The amount of isocyanate employed will depend upon the density of thefoam and the amount of cross-linking desired. In general the total —NCOequivalent to total active hydrogen equivalent (i.e., hydroxyl pluswater, if water is present) should be such as to provide a ratio of 0.8to 1.2 equivalents of —NCO per equivalent of active hydrogen, andpreferably a ratio of about 1.0 to 1.1 equivalents of —NCO per reactivehydrogen.

Foaming can be accomplished by employing a small amount of water in thereaction mixture (for example, from about 0.5 to 5 weight percent ofwater, based on total weight of the reaction mixture), or through theuse of blowing agents which are vaporized by the exotherm of theisocyanate-reactive hydrogen reaction, or by a combination of the twomethods. All of these methods are known in the art. The curing stepcomprises maintaining the polyurethane foam at an elevated temperatureup to about 200° C. and in an oxygen-containing atmosphere for asufficient time period to increase the degree of cross-linking of thepolymers present in the foam. Moreover, unreacted constituents areeliminated from the foam at this time. The curing time is dependent onthe particular polyurethane foam employed, the curing temperature, thedegree of cross-linking present in the foam prior to curing, etc. Thecuring time can range from about 2 hours to about 64 hours.

The oxidizing step comprises maintaining the foam at a temperature inthe range from about 200° C. to about 255° C. and in anoxygen-containing atmosphere for a sufficient time period to bring abouta weight loss of the foam of at least about 3.5 percent. During thisstep some oxidation of the foam structure is believed to take place. Itis important that the temperature is maintained with in the aforesaidlimits since otherwise the foam fuses, collapses, and becomes distorted.

The pyrolyzing step comprises maintaining the foam, at a temperature inthe range from about 500° C. to about 1000° C. for a sufficient timeperiod to produce a homogeneous, porous matrix consisting substantiallyof carbon. The pyrolyzing step is carried out in an oxygen-freeatmosphere, such as a vacuum or an inert gas atmosphere comprisingnitrogen, argon, krypton, xenon, helium, and the like. As a generalrule, the pyrolyzing temperature should exceed the temperature at whichthe resultant product is to be used.

In some embodiments, a graphitization heat treatment is then carried outat a temperature above about 2200° C. and in an oxygen-free atmosphere.A graphitization temperature in the range from about 2800° C. to about3000° C. is preferred. The temperature and the duration of thegraphitization treatment are dependent on the degree of graphitizationdesired and also on the physical size of the carbon foam piece beinggraphitized. The time period at the aforesaid temperatures can be asshort as five minutes and as long as eight hours. In most instances atime period of about thirty minutes is sufficient for completegraphitization.

Acrylonitrile Foams

In another embodiment, a carbon foam useful as the substrate inaccordance with this disclosure is prepared by dissolving a carbonizablepolymer or copolymer in a solvent at a temperature sufficient to effectcomplete dissolution. The polymer or copolymer comprisesacrylonitrile-based polymers, such as polyacrylonitrile (PAN), andacrylonitrile based copolymers, such as polyacrylonitrile-co-maleicanhydride. In other embodiments, other suitable carbonizable polymerscan be employed, including phenolics, guargums, polyesters,poly(furfuryl alcohol), polyimides, cellulose polymers (such as Rayon),polyamides, polyacrylethers, polyphenylenes, polyacenaphthalenes,polytriadiazoles and polyvinylpyridines.

The dissolution of the carbonizable polymeric materials in the solventcan be carried out at a temperature of from about 100 to about 200° C.After dissolution of the polymer or copolymer, the solution is pouredinto a mold and is then cooled. A typical cooling rate or quench isabout 10° C. per minute. After the quench, the solvent is removed fromthe solution and the polymer or copolymer can be carbonized to producethe foams of the present disclosure.

In some embodiments, the solvent is chosen so that liquid phaseseparation occurs during the quench. The dissolved polymeric solution iscooled in the mold so that liquid phase separation occurs. Cooling maybe continued until the solvent freezes in which case the solvent isremoved by sublimation under vacuum (freeze-drying). If the solvent isnot frozen, then it may be removed by extraction. The isotropic lowdensity, open-celled microcellular carbon foam is then produced bycarbonizing the desired polymeric materials following removal of thesolvent. Suitable solvents for freeze-drying to be used in thepreparation of the isotropic foams include: maleic anhydride, 70-90%methylsulfone with 10-30% cyclohexanol, 85-95% methyl sulfone with 5-15%water, and 40-60% methyl sulfone with 60-40% norcamphor (all solventpercentages are given as wt/wt except for aqueous methyl sulfone, whichis given as wt/volume). Preferred solvents which can be extracted toprepare isotropic foams are: 75-95% dimethyl formamide with 5-25% water(volume/volume), 70-90% dimethyl formamide with 10-30% ethylene glycol,70-90% 1-methyl-2-pyrrolidone with 10-30% ethylene glycol and 40-65%succinonitrile with 35-60% maleic anhydride.

The carbonizable polymeric materials prepared as indicated above can becarbonized in a high temperature oven. Various carbonization schemes arepossible, including pretreating after removal of solvent and beforecarbonizing by subjecting the foam to an oxygen or air atmosphere forabout 12-24 hours at temperatures of from about 180-260° C. Thispreliminary step allows a higher graphitic carbon content in the finalcarbonized foam. Following the pretreatment, the polymeric materialscan, in certain embodiments, be heated to a temperature of from about500-2500° C. for about 6-10 hours in the presence of an inert gas.Carbonization can be carried out by heating the foams slowly (5° C. perminute) under a continuous flow of the inert gas. The gas used in someembodiments is argon, but other inert gases such as nitrogen, neon,krypton or xenon are also suitable. During this heating process, thefoams will shrink and therefore densify to an extent depending upon thecarbonization scheme. This effect can be offset by making the startingpolymer foam at a lower density than required in the resulting carbonfoam.

Organic Gels

In another embodiment, carbon foam substrates can be prepared by hightemperature pyrolysis of a low density open cell organic foam composite,which is prepared from a suitable substrate and an organic gel, by:

(a) forming a reaction mixture comprising one or more hydroxylatedbenzene compounds, one or more aldehydes, one or more catalysts, andwater, wherein the molar ratio of the hydroxylated benzene compounds tothe catalysts in the reaction mixture is greater than about 1000; and,(b) infusing a porous carbon substrate or a porous organic substrate(e.g., a fiber or sheet) with the reaction mixture to form an infusedcarbon or porous organic substrate;(c) heating the infused porous substrate at a gelation temperature for agelation time to form an organic gel/porous substrate composite;(d) heating the organic gel/porous substrate composite at a curingtemperature for a curing time to form a cured organic gel/poroussubstrate composite;(e) drying the cured organic gel/porous substrate composite to form anorganic foam/porous substrate composite; and,(f) pyrolyzing the organic foam/porous substrate composite at apyrolysis temperature to form a carbon foam/carbon substrate composite.

While certain embodiments of carbon foams useful as a catalyticconverter substrate in accordance with this disclosure have been taught,any carbon foam having the desired characteristics can be employed. Forinstance, regardless of the starting foam, the GSA of the substrate ofthe present disclosure is at least about 5000 m²/m³ and can be at leastabout 8000 m²/m³, or even at least 15,000 m²/m³ or higher, and, inembodiments, is up to about 35,000 m²/m³. Thus, in some embodiments, theGSA of the substrate carbon foam can range from about 5000 m²/m³ toabout 35,000 m²/m³, or 8000 m²/m³ to about 35,000 m²/m³, or even 15,000m²/m³ to about 35,000 m²/m³.

Likewise, in certain embodiments, the carbon foam for use as a substratefor catalytic converters has a density of about 0.03 to about 0.9 gramsper cubic centimeter (g/cc), with a surface area of about 200 to about900 square meters per gram (m²/g), and the compressive strength of thefoam should be at least about 35 kilograms per square centimeter(kg/cm²)(measured by, for instance, ASTM C695).

The use of the foam substrate of this disclosure should create apressure drop of no greater than about 300 Pa, and, in embodiments, fromabout 25 to about 300 Pa regardless of the carbon foam startingmaterial; in certain embodiments, the pressure drop should be no greaterthan about 90 Pa, and can be from about 50 to about 90 Pa. In otherembodiments, the foam substrate of this disclosure should lead to apressure drop of no greater than 80% of the pressure drop observed whena conventional catalytic converter is employed in its place. The when acarbon foam in accordance with this disclosure is used in a catalyticconverter, it should provide a pressure drop of no greater than 120 Paat an exhaust velocity of 0.025 m³/s. In certain embodiments thepressure drop is less than 90 Pa.

In some embodiments, regardless of the specific nature of the startingfoam, the carbon foam useful as a catalytic converter substrate exhibitsa permeability of at least about 8.0 darcys; in other embodiments thecarbon foam has a permeability of at least than about 15.0 darcys (asmeasured, for instance, by ASTM C577). In yet other embodiments, thecarbon foam of this disclosure exhibits a permeability of at least about20.0 darcys. From a practical standpoint, the foam has a permeability offrom about 15.0 darcys to about 35.0 darcys.

The carbon foams described herein can, in some embodiments, be formedinto two- or three-way catalytic converters by conventional methodswhich are known to the skilled artisan. For instance, in certainembodiments, three-way catalytic converters can be prepared using thedescribed carbon foam substrates by separately mixing oxidative preciousmetals, such as platinum or palladium, with aluminum oxide, water, andother components to make a slurry in one container and mixing reductiveprecious metals, such as rhodium, with cerium, zirconium oxide, water,and other components to make a second slurry in a second container. Theslurries are normally referred to as oxidative and reductive washcoats.In some embodiments, the oxidative washcoat includes anywhere from about25% to about 75% of the oxidative precious metals; the reductivewashcoat includes anywhere from 5% to about 50% of the reductiveprecious metals.

The carbon foam is dipped into one of the washcoats to form a firstcatalytic layer on and throughout the foam. After drying and calcining,the carbon foam substrate is dipped into the other washcoat to form asecond layer. The carbon foam including the two washcoat layers isfitted into a shell of a catalytic converter, which connects to theengine for treating exhaust gas.

In other embodiments, the precious metals can be incorporated into thestarting materials used to form the carbon foams of this disclosure. Forinstance, the precious metals, such as platinum or palladium, withaluminum oxide, and rhodium with cerium and zirconium oxide, can beincorporated into the phenolic, polyurethane, or polyester resin, or theacrylonitrile-based polymers, or the organic gel, from which the carbonfoam is formed. In this manner, the catalyst materials are presentwithin the struts/walls of the carbon foam substrate, which can increasecontact with the exhaust gases and could reduce the amount of catalystneeded.

In another embodiment, the catalyst material can comprise non-noblemetal nano-scale catalyst particles, as described, for instance, in USPatent Application Publication Nos. 2010/0222214, 2007/0286778,2007/0283782, and 2007/0036913. Non-noble metals are metals other thanthe noble metals; the noble metals are generally considered to be gold,silver, platinum, palladium, iridium, rhenium, mercury, ruthenium, andosmium. Thus, less costly metals, such as iron, nickel, and manganese,can be employed as the catalyst in the catalytic converter, reducing thecost of manufacture. By nano-scale particles is meant particles havingan average diameter of no greater than about 1,000 nanometers (nm),e.g., no greater than about one micron. More preferably, the particleshave an average diameter no greater than about 250 nm, most preferablyno greater than about 20 nm.

The nano-scale particles can be roughly spherical or isotropic, meaningthey have an aspect ratio of about 1.4 or less, although particleshaving a higher aspect ratio can also be prepared and used as catalystmaterials. Aspect ratio refers to the ratio of the largest dimension ofthe particle to the smallest dimension of the particle (thus, a perfectsphere has an aspect ratio of 1.0).

Where nano-scale non-noble metal catalysts are employed, they can beincorporated into the washcoats described above, in full or partialreplacement of or in addition to the “conventional” precious metalcatalysts. Additionally, the non-noble metal catalysts can also beincorporated into the starting materials used to form the carbon foamsof this disclosure, again, in full or partial replacement of or inaddition to the “conventional” precious metal catalysts.

In one embodiment for producing nano-scale particles, a decomposablenon-noble metal-containing moiety is fed into a reactor vessel andsufficient energy to decompose the moiety applied, such that the moietydecomposes and non-noble metal nano-scale particles are deposited on asupport or collected by a collector. The decomposable moiety used in theinvention can be any decomposable non-noble metal-containing material,including an organometallic compound, a metal complex or a metalcoordination compound, provided that the moiety can be decomposed toprovide free metals, such that the free metal can be deposited on asupport or collected by a collector. In certain embodiments, thedecomposable moiety comprises one or more non-noble metal carbonyls,such as nickel or iron carbonyls.

The particular decomposable moiety or moieties employed depends on thecatalyst particle desired to be produced. In other words, if the desirednano-scale catalyst particles comprise nickel and iron, the decomposablemoieties employed can be nickel carbonyl, Ni(CO)₄, and iron carbonyl,Fe(CO)₅. In addition, polynuclear metal carbonyls such as diironnonacarbonyl, Fe₂(CO)₉, triiron dodecycarbonyl, Fe₃(CO)₁₂,decacarbonyldimanganese, Mn₂(CO)₁₀ can be employed in the production ofnano-scale catalyst particles in accordance herewith. The polynuclearmetal carbonyls can be particularly useful where the nano-scale catalystparticles desired are alloys or combinations on more than one metallicspecie.

Generally speaking, carbonyls are transition metals combined with carbonmonoxide and have the general formula M_(x)(CO)_(y), where M is a metalin the zero oxidation state and where x and y are both integers. Whilemany consider metal carbonyls to be coordination compounds, the natureof the metal to carbon bond leads some to classify them asorganometallic compounds.

The metal carbonyls useful in producing nano-scale catalyst particlescan be prepared by a variety of methods, many of which are described in“Kirk-Othmer Encyclopedia of Chemical Technology,” Vol. 5, pp. 131-135(Wiley Interscience 1992). For instance, metallic nickel and iron canreadily react with carbon monoxide to form nickel and iron carbonyls,and it has been reported that cobalt, molybdenum and tungsten can alsoreact carbon monoxide, albeit under conditions of higher temperature andpressure. Other methods for forming metal carbonyls include thesynthesis of the carbonyls from salts and oxides in the presence of asuitable reducing agent (indeed, at times, the carbon monoxide itselfcan act as the reducing agent), and the synthesis of metal carbonyls inammonia. In addition, the condensation of lower molecular weight metalcarbonyls can also be used for the preparation of higher molecularweight species, and carbonylation by carbon monoxide exchange can alsobe employed.

The synthesis of polynuclear and heteronuclear metal carbonyls,including those discussed above, is usually effected by metathesis oraddition. Generally, these materials can be synthesized by acondensation process involving either a reaction induced bycoordinatively unsaturated species or a reaction between coordinativelyunsaturated species in different oxidation states. Although highpressures are normally considered necessary for the production ofpolynuclear and heteronuclear carbonyls (indeed, for any metal carbonylsother than those of transition metals), the synthesis of polynuclearcarbonyls, including manganese, ruthenium and iridium carbonyls, underatmospheric pressure conditions is also believed feasible.

The production process for nano-scale metal particles is advantageouslypracticed in an apparatus comprising a reactor vessel, at least onefeeder for feeding or supplying the decomposable moiety into the reactorvessel, a support or collector which is operatively connected to thereactor vessel for deposit thereon or collection thereby of nano-scalecatalyst particles produced on decomposition of the decomposable moiety,and a source of energy capable of decomposing the decomposable moiety.The source of energy should act on the decomposable moiety such that themoiety decomposes to provide nano-scale metal particles which aredeposited on the support or collected by the collector.

The support or collector can be any material on which the non-noblemetal nano-scale catalyst particles produced from decomposition of thedecomposable moieties can be deposited or in which they can becollected; in one embodiment, the collector can be a centrifugal orcyclonic collector.

The energy employed to decompose the decomposable moiety can be any formof energy capable of accomplishing this function. For instance,electromagnetic energy such as infrared, visible, or ultraviolet lightof the appropriate wavelengths can be employed. Additionally, microwaveand/or radio wave energy, or other appropriate forms of energy can alsobe employed (example, a spark to initiate “explosive” decompositionassuming suitable moiety and pressure), provided the decomposable moietyis decomposed by the energy employed. Thus, microwave energy, at afrequency of about 2.4 gigahertz (GHz) or induction energy, at afrequency which can range from as low as about 180 hertz (Hz) up to ashigh as about 13 mega Hz can be employed. A skilled artisan wouldreadily be able to determine the form of energy useful for decomposingthe different types of decomposable moieties which can be employed.

One preferred form of energy which can be employed to decompose thedecomposable moiety is heat energy supplied by, e.g., heat lamps,radiant heat sources, or the like. Heat can be especially useful forhighly volatile moieties, such as non-noble metal carbonyls. In suchcase, the temperatures needed are no greater than about 250° C. Indeed,generally, temperatures no greater than about 200° C. are needed todecompose the decomposable moiety and produce nano-scale catalystparticles therefrom.

By controlling the nature of the decomposable moiety introduced into thereactor vessel used in the production of nano-scale particles, throughfeeders, the rate of feeding of each decomposable moiety, and the orderin which different species are fed into the reactor vessel, the catalystparticles produced can be controlled. By this is meant a significantlyhigher percentage of the specific desired catalyst particle (referred toas the principal particle) is produced. For example, if a catalystparticle containing a ratio of nickel atoms to iron atoms to manganeseatoms of 3:2:2 is desired, a higher percentage of 3:2:2 particles willbe produced (as compared to, for instance, 3:3:3 or 1:1:3, etc.particles).

In another embodiment, chain agglomerations of nano-scale metalparticles can be produced, which comprise hundreds, or even thousands,of nano-scale metal particles organized in an elongate arrangement (asopposed to a spherical or cluster arrangement), and can appear to thenaked eye as fibrous in nature. More particularly, each chainagglomeration of nano-scale metal particles has an aspect ratio, thatis, ratio of major dimension (i.e., length) to minor dimension (i.e.,width or diameter) of at least about 700:1, more advantageously at leastabout 900:1. As such, the surface area of the nano-scale metal particlechain agglomerations makes the agglomerations uniquely effective inapplications such as catalysis. Indeed, such chain agglomerations can beespecially useful in a catalytic converter in accordance with thisdisclosure, as they can extend into the exhaust stream to increasecatalytic contact.

The production of chain agglomerations is advantageously practiced in anapparatus comprising a reactor vessel, at least one feeder for feedingor supplying the decomposable moiety into the reactor vessel, a supportor collector which is operatively connected to the reactor vessel fordeposit or collection of nano-scale metal particles produced ondecomposition of the decomposable moiety, and a source of energy capableof decomposing the decomposable moiety. The source of energy should acton the decomposable moiety such that the moiety decomposes to providenano-scale metal particles which are deposited on the support orcollected by the collector.

The reactor vessel can be formed of any material which can withstand theconditions under which the decomposition of the moiety occurs.Generally, where the reactor vessel is a closed system, that is, whereit is not an open ended vessel permitting reactants to flow into and outof the vessel, the vessel can be under subatmospheric pressure, by whichis meant pressures as low as about 250 millimeters (mm) Hg. Indeed, theuse of subatmospheric pressures, as low as about 1 mm Hg of pressure,can accelerate decomposition of the decomposable moiety and providesmaller nano-scale particles. However, one advantage of the invention isthe ability to produce nano-scale particles at generally atmosphericpressure, i.e., about 760 mm Hg. Alternatively, there may be advantagein cycling the pressure, such as from sub-atmospheric to generallyatmospheric or above, to encourage nano-deposits within the structure ofthe particles or supports. Of course, even in a so-called “closedsystem,” there needs to be a valve or like system for relieving pressurebuild-up caused, for instance, by the generation of carbon monoxide (CO)or other by-products. Accordingly, the use of the expression “closedsystem” is meant to distinguish the system from a flow-through type ofsystem as discussed hereinbelow.

When the reactor vessel is a “flow-through” reactor vessel, that is, aconduit through which the reactants flow while reacting, the flow of thereactants can be facilitated by drawing a partial vacuum on the conduit,although no lower than about 250 mm Hg is necessary in order to draw thereactants through the conduit towards the vacuum apparatus, or a flow ofan inert gas such as nitrogen or argon can be pumped through the conduitto thus carry the reactants along the flow of the inert gas.

Indeed, the flow-through reactor vessel can be a fluidized bed reactor,where the reactants are borne through the reactor on a stream of afluid. This type of reactor vessel may be especially useful where thenano-scale metal particles produced are intended to be loaded on supportmaterials, like carbon blacks or the like, or where the metal particlesare to be loaded on an ion exchange or similar resinous material.

The at least one feeder supplying the decomposable moiety into thereactor vessel can be any feeder sufficient for the purpose, such as aninjector which carries the decomposable moiety along with a jet of a gassuch as an inert gas like argon or nitrogen, to thereby carry thedecomposable moiety along the jet of gas through the injector nozzle andinto the reactor vessel. The gas employed can be a reactant, like oxygenor ozone, rather than an inert gas. This type of feeder can be usedwhether the reactor vessel is a closed system or a flow-through reactor.

Supports useful in the practice of the invention can be any material onwhich the nano-scale metal particles produced from decomposition of thedecomposable moieties can be deposited.

The support or collector can be disposed within the reactor vessel(indeed this is required in a closed system and is practical in aflow-through reactor). However, in a flow-through reactor vessel, theflow of reactants can be directed at a support positioned outside thevessel, at its terminus, especially where the flow through theflow-through reactor vessel is created by a flow of an inert gas.Alternatively, in a flow-through reactor, the flow of nano-scale metalparticles produced by decomposition of the decomposable moiety can bedirected into a centrifugal or cyclonic collector which collects thenano-scale particles in a suitable container for future use.

Depending on the source of energy employed, the reactor vessel should bedesigned so as to not cause deposit of the nano-scale metal particles onthe vessel itself (as opposed to the collector) as a result of theapplication of the source of energy. In other words, if the source ofenergy employed is heat, and the reactor vessel itself becomes heated toa temperature at or somewhat higher than the decomposition temperatureof the decomposable moiety during the process of applying heat to thedecomposable moiety to effect decomposition, then the decomposablemoiety will decompose at the walls of the reactor vessel, thus coatingthe reactor vessel walls with nano-scale metal particles rather thancollecting the nano-scale metal particles with the collector (oneexception to this general rule occurs if the walls of the vessel are sohot that the decomposable moiety decomposes within the reactor vesseland not on the vessel walls, as discussed in more detail below).

One way to avoid this is to direct the energy directly at the collector.For instance, if heat is the energy applied for decomposition of thedecomposable moiety, the support or collector can be equipped with asource of heat itself, such as a resistance heater in or at a surface ofthe support or collector such that the support or collector is at thetemperature needed for decomposition of the decomposable moiety and thereactor vessel itself is not. Thus, decomposition occurs at the supportor collector and formation of nano-scale particles occurs principally atthe support or collector. When the source of energy employed is otherthan heat, the source of energy can be chosen such that the energycouples with the support or collector, such as when microwave orinduction energy is employed. In this instance, the reactor vesselshould be formed of a material which is relatively transparent to thesource of energy, especially as compared to the support or collector.

For the production of the chain agglomerations, the source of heat isadvantageously a resistance heater, such as a wire, disposed within theflow of decomposable moieties. The heated wire provides a point ofcontact for the decomposition of decomposable moieties to formnano-scale metal particles; additional decomposition then occurs on thepreviously formed particles, and continues as chains of nano-scale metalparticles are formed from these initial particles produced on the wire.While the precise mechanism for this phenomenon is not fully understood,it is believed that decomposition of decomposable moieties to producenano-scale metal particles occurs by conduction along the chain as itforms. In other words, nano-scale metal particles are formed on thewire, which then cause further decomposition of decomposable moietiesthereon by heat conduction along the metal particles formed on the wire,and so on.

Especially in situations when the support or collector is disposedoutside the reactor vessel when a flow-through reactor vessel isemployed with a support or collector at its terminus (whether a solidsubstrate collector for depositing of nano-scale metal particles thereonor a cyclonic or like collector for collecting the nano-scale metalparticles for a suitable container), the decomposition of thedecomposable moiety occurs as the moiety is flowing through theflow-through reactor vessel and the reactor vessel should be transparentto the energy employed to decompose the decomposable moiety.

Alternatively, whether or not the support or collector is inside thereactor vessel, or outside it, the reactor vessel can be maintained at atemperature below the temperature of decomposition of the decomposablemoiety, where heat is the energy employed. One way in which the reactorvessel can be maintained below the decomposition temperatures of themoiety is through the use of a cooling medium like cooling coils or acooling jacket. A cooling medium can maintain the walls of the reactorvessel below the decomposition temperatures of the decomposable moiety,yet permit heat to pass within the reactor vessel to heat thedecomposable moiety and cause decomposition of the moiety and productionof nano-scale metal particles.

In an alternative embodiment which is especially applicable where boththe walls of the reactor vessel and the gases in the reactor vessel aregenerally equally susceptible to the heat energy applied (such as whenboth are relatively transparent), heating the walls of the reactorvessel, when the reactor vessel is a flow-through reactor vessel, to atemperature substantially higher than the decomposition temperature ofthe decomposable moiety can permit the reactor vessel walls tothemselves act as the source of heat. In other words, the heat radiatingfrom the reactor walls will heat the inner spaces of the reactor vesselto temperatures at least as high as the decomposition temperature of thedecomposable moiety. Thus, the moiety decomposes before impacting thevessel walls, forming nano-scale particles which are then carried alongwith the gas flow within the reactor vessel, especially where the gasvelocity is enhanced by a vacuum. This method of generatingdecomposition heat within the reactor vessel is also useful where thenano-scale particles formed from decomposition of the decomposablemoiety are being attached to carrier materials (like carbon black) alsobeing carried along with the flow within the reactor vessel. In order toheat the walls of the reactor vessel to a temperature sufficient togenerate decomposition temperatures for the decomposable moiety withinthe reactor vessel, the walls of the reactor vessel are preferablyheated to a temperature which is significantly higher than thetemperature desired for decomposition of the decomposable moiety(ies)being fed into the reactor vessel, which can be the decompositiontemperature of the decomposable moiety having the highest decompositiontemperature of those being fed into the reactor vessel, or a temperatureselected to achieve a desired decomposition rate for the moietiespresent. For instance, if the decomposable moiety having the highestdecomposition temperature of those being fed into the reactor vessel isnickel carbonyl, having a decomposition temperature of about 50° C.,then the walls of the reactor vessel should preferably be heated to atemperature such that the moiety would be heated to its decompositiontemperature several (at least three) millimeters from the walls of thereactor vessel. The specific temperature is selected based on internalpressure, composition and type of moiety, but generally is not greaterthan about 250° C. and is typically less than about 200° C. to ensurethat the internal spaces of the reactor vessel are heated to at least50° C.

In any event, the reactor vessel, as well as the feeders, can be formedof any material which meets the requirements of temperature and pressurediscussed above. Such materials include a metal, graphite, high densityplastics or the like. Most preferably the reactor vessel and relatedcomponents are formed of a transparent material, such as quartz or otherforms of glass, including high temperature glass commercially availableas Pyrex® materials.

In one embodiment of the process of this disclosure, a single feederfeeds a single decomposable moiety into the reactor vessel for formationof nano-scale metal particles. In another embodiment, however, aplurality of feeders each feeds decomposable moieties into the reactorvessel. In this way, all feeders can feed the same decomposable moietyor different feeders can feed different decomposable moieties, such asadditional metal carbonyls, so as to provide nano-scale particlescontaining different metals such as platinum-nickel combinations ornickel-iron combinations as desired, in proportions determined by theamount of the decomposable moiety fed into the reactor vessel. Forinstance, by feeding different decomposable moieties through differentfeeders, one can produce a nano-scale particle having a core of a firstmetal, with domains of a second or third, etc. metal coated thereon.Indeed, altering the decomposable moiety fed into the reactor vessel byeach feeder can alter the nature and/or constitution of the nano-scaleparticles produced. In other words, if different proportions of metalsmaking up the nano-scale particles, or different orientations of themetals making up the nano-scale particles is desired, altering thedecomposable moiety fed into the reactor vessel by each feeder canproduce such different proportions or different orientations.

Indeed, in the case of the flow-through reactor vessel, each of thefeeders can be arrayed about the circumference of the conduit formingthe reactor vessel at approximately the same location, or the feederscan be arrayed along the length of the conduit so as to feeddecomposable moieties into the reactor vessel at different locationsalong the flow path of the conduit to provide further control of thenano-scale particles produced.

In an embodiment, this disclosure includes a process for reducingdisadvantageous emissions from a vehicle exhaust, where the processincludes providing the carbon foam described above, applying oxidativeand reductive washcoats to the carbon foam, wherein the oxidative andreductive washcoats include precious metals, non-noble metal nano-scaleparticles, or combinations thereof, fitting the carbon foam into a shellto form a catalytic converter, and connecting the catalytic converter toa vehicle engine for treating exhaust gas. The catalytic converter canbe connected to the vehicle engine by being positioned in the tailpipesuch that exhaust gases flow therethrough. In yet another embodiment,this disclosure includes a process for reducing disadvantageousemissions from a vehicle exhaust which includes providing the carbonfoam described above, having catalytic metals incorporated thereinto,wherein the catalytic metals can be precious metals, non-noble metalnano-scale particles, or combinations thereof, fitting the carbon foaminto a shell to form a catalytic converter, and connecting the catalyticconverter to a vehicle engine for treating exhaust gas. The catalyticconverter can be connected to the vehicle engine by being positioned inthe tailpipe such that exhaust gases flow therethrough.

The catalytic converter substrates in accordance with this disclosurecan provide emissions reduction equivalent to or even better thanconventional catalytic converters, while potentially reducing pressuredrop and the amount of catalyst metal employed. Catalyst loading on thecarbon foam substrate of the present disclosure can be as low as 55g/ft³, and can range as high as 325 g/ft³ depending on the engine andperformance characteristics desired. In some embodiments, catalystloading is between about 65 g/ft³ and about 275 g/ft³; in otherembodiments, catalyst loading is between about 80 g/ft³ and about 250g/ft³.

As such, use of the disclosed carbon foam substrates, and catalyticconverters can potentially meet or exceed emissions reductionrequirements while simultaneously increasing horsepower and engineefficiency because of the reduced pressure drop. And, in someembodiments these advantages can be achieved at a lower cost.

All references cited in this specification, including withoutlimitation, all patents, patent applications, and publications, and thelike, are hereby incorporated by reference into this specification intheir entireties. The discussion of the references herein is intendedmerely to summarize the assertions made by their authors and noadmission is made that any reference constitutes prior art. Applicantreserves the right to challenge the accuracy and pertinence of the citedreferences.

Although embodiments of the disclosure have been described usingspecific terms, devices, and methods, such description is forillustrative purposes only. The words used are words of descriptionrather than of limitation. It is to be understood that changes andvariations may be made by those of ordinary skill in the art withoutdeparting from the spirit or the scope of the present disclosure, whichis set forth in the following claims. In addition, it should beunderstood that aspects of the various embodiments may be interchangedin whole or in part. For example, while methods for the production of acommercially sterile liquid nutritional supplement made according tothose methods have been exemplified, other uses are contemplated.Therefore, the spirit and scope of the appended claims should not belimited to the description of the versions contained therein.

What is claimed is:
 1. A process for reducing disadvantageous emissionsfrom a vehicle exhaust, comprising providing an open cell carbon foamhaving a geometric surface area of at least about 15,000 m²/m³ and apermeability of at least about 15.0 darcys, applying oxidative andreductive washcoats to the carbon foam, wherein the oxidative andreductive washcoats comprise precious metals, non-noble metal nano-scaleparticles, or combinations thereof, fitting the carbon foam into a shellto form a catalytic converter, and connecting the catalytic converter toa vehicle engine for treating exhaust gas.
 2. The process of claim 1,wherein the catalytic converter is connected to the vehicle engine bybeing positioned in a tailpipe such that exhaust gases flowtherethrough.
 3. The process of claim 2, wherein the catalytic convertercreates a pressure drop of no greater than 120 Pa when gas flows throughat a velocity of 0.025 m³/s.
 4. The process of claim 1, wherein thecarbon foam is formed from foam starting materials selected from thegroup consisting of phenolic foam, polyurethane foam, polyacrylonitrile,other acrylonitrile materials, and foams derived from organic gels.
 5. Aprocess for reducing disadvantageous emissions from a vehicle exhaust,comprising: (a) providing an open cell carbon foam having catalyticmetals incorporated thereinto, wherein the catalytic metals compriseprecious metals, non-noble metal nano-scale particles, or combinationsthereof, and further wherein the carbon foam has a geometric surfacearea of at least about 15,000 m²/m³ and a permeability of at least about15.0 darcys, (b) fitting the carbon foam into a shell to form acatalytic converter, and (c) connecting the catalytic converter to avehicle engine for treating exhaust gas.
 6. The process of claim 5,wherein the catalytic converter is connected to the vehicle engine bybeing positioned in a tailpipe such that exhaust gases flowtherethrough.
 7. The process of claim 5, wherein the catalytic convertercreates a pressure drop of no greater than 120 Pa when gas flows throughat a velocity of 0.025 m³/s.
 8. The process of claim 1, wherein thenon-noble metal nano-scale catalyst particles comprise iron, nickel,manganese, and combinations thereof.
 9. The process of claim 1, whereinthe non-noble metal nano-scale catalyst particles have an averagediameter of no greater than about 20 nm.
 10. The process of claim 1,wherein the non-noble metal nano-scale catalyst particles are present inchain agglomerations which have an aspect ratio of at least 700:1. 11.The process of claim 1, wherein the catalytic converter creates apressure drop of no greater than 90 Pa when gas flows through at avelocity of 0.025 m³/s.
 12. The process of claim 1, wherein catalystloading is between about 55 g/ft³ and about 325 g/ft.
 13. The process ofclaim 5, wherein the non-noble metal nano-scale catalyst particlescomprise iron, nickel, manganese, and combinations thereof.
 14. Theprocess of claim 5, wherein the non-noble metal nano-scale catalystparticles have an average diameter of no greater than about 20 nm. 15.The process of claim 5, wherein the non-noble metal nano-scale catalystparticles are present in chain agglomerations which have an aspect ratioof at least 700:1.
 16. The process of claim 5, wherein the catalyticconverter creates a pressure drop of no greater than 90 Pa when gasflows through at a velocity of 0.025 m³/s.
 17. The process of claim 5,wherein catalyst loading is between about 55 g/ft and about 325 g/ft.